Perpendicular magnetic recording head laminated with AFM-FM phase change material

ABSTRACT

A PMR writer is disclosed that minimizes pole erasure during non-writing and maximize write field during writing through an AFM-FM phase change material that is in an anti-ferromagnetic (AFM) state during non-writing and switches to a ferromagnetic (FM) state by heating during writing. The main pole layer including the write pole may be comprised of a laminated structure having a plurality of “n” ferromagnetic layers and “n−1” AFM-FM phase change material layers arranged in an alternating manner. The AFM-FM phase change material is preferably a FeRh, FeRhPt, FeRhPd, or FeRhIr and may also be used as a flux gate to prevent yoke flux from leaking into the write pole tip. Heating for the AFM to FM transition is provided by write coils and/or a coil located near the AFM-FM phase change material to enable faster transition times.

This is a Divisional application of U.S. patent application Ser. No.11/894,494, filed on Aug. 21, 2007, now U.S. Pat. No. 8,004,794 B2,which is herein incorporated by reference in its entirety, and assignedto a common assignee.

FIELD OF THE INVENTION

The invention relates to a main pole layer of a PMR writer and inparticular to an antiferromagnetic (AFM)-ferromagnetic (FM) phase changematerial that may be employed in the write pole tip and/or the yoke tominimize data erasure after a write operation without significantlyreducing the write field during a write operation.

BACKGROUND OF THE INVENTION

Perpendicular magnetic recording (PMR) has become the mainstreamtechnology for disk drive applications beyond 200 Gbit/in², replacinglongitudinal magnetic recording (LMR) devices. Due to the continuingreduction of transducer size, high moment soft magnetic thin films witha Bs above 22 kG are required for write head applications. A PMR headwhich combines the features of a single pole writer and a double layeredmedia has a great advantage over LMR in providing higher write field,better read back signal, and potentially much higher areal density. Inparticular, a shielded pole head can provide a large head field gradientat the trailing side due to the presence of a trailing shield andsubstantially improve the write performance.

Perpendicular recording demands increasingly smaller pole tip size inthe magnetic recording heads to achieve higher data density on themagnetic medium. However, prior studies have shown that theperpendicular direction shape anisotropy in the smaller writer pole tipsmay lead to serious pole erasure (PE). In other words, a remanentmagnetic field can exist in the write pole tip after the write currentis turned off thereby leading to data erasure in the magnetic mediumduring non-write operations. References related to this subject are (1)K. Hirata et al., “A study of pole material properties for pole erasuresuppression in perpendicular recording heads”, J. Magn. Magn. Mat., Vol.287, pp. 352-356, November 2004; (2) Y. Zhou et al., “Perpendicularwrite head remanence characterization using a contact scanning recordingtester”, J. Appl. Phys., Vol. 97, 10N903 (2005); and (3) Y. Zhou andJ.-G. Zhu, “Dependence of the pole tip remanence on the mediummagnetization state underneath the trailing shield of a perpendicularwrite head”, J. App. Phys. Vol. 97, 10N518 (2005).

To alleviate the PE problem, two approaches are described by D. Bai etal. in “Writer pole tip remanence in perpendicular recording”, IEEETrans. Magn., Vol. 42, p. 473 (2006) and typically involve making thewriter head into a laminated multi-layered structure through dry filmdeposition methods. According to a first method, making the write headinto a laminated multi-layer structure where thicker magnetic layers areseparated by thinner non-magnetic layers, the magneto-static couplingfield between the adjacent layers through the edge charges will help thewrite pole maintain a near zero net magnetic moment when the writecurrent is turned off. The inter-layer magneto-static coupling prefersan anti-parallel magnetization orientation of adjacent magnetic layerswhich leads to charge cancellation between the adjacent magnetic layersand to a net zero magnetic charge from the write pole tip as a whole.The second approach is similar to the first. However, the thin spacerlayer between neighboring magnetic layers is chosen from a specificmetal such as Ru or Cr and has a specific thickness. Thus, due to theRuderman-Kittel-Kasuya-Yoshida (RKKY) interaction between localizedmoments mediated by the conduction electrons of the spacer metal, an AFMexchange coupling between the adjacent magnetic layers can beestablished. This AFM coupling field is usually much higher than themagneto-static coupling field involved in the first approach andtherefore is more effective in reducing the PE field in perpendicularwrite heads.

Unfortunately, reducing the PE field with either magneto-static couplingor AFM coupling results in a loss in writability (write field) andparticularly near the trailing edge of the write pole tip. The couplingfield that minimizes PE also reduces the write field through the sameinteractions. In addition, a non-magnetic spacer layer causes a furtherdecrease in write field because of a reduced volume of magnetic materialin the write pole. Thus, a trade off exists between reducing the PEfield during non-write operations and maintaining a strong write fieldduring the writing process in state of the art PMR technology.

It is known in the prior art that FeRh has an abrupt first ordertransition from an AFM phase to a FM phase without structural change ata rather low temperature of 330° K to 350° K. This abrupt phase changeis thought to be associated with a CsCl type bodied centered cubic (bcc)Fe₅₀Rh₅₀ alloy. References include the following: J. Lommel and J.Kouvel, “Effects of mechanical and thermal treatment on the structureand magnetic transitions of FeRh”, J. Appl. Phys., Vol. 38, pp.1263-1264, March 1967; Y. Ohtani and I. Hatakeyama,“Antiferro-ferromagnetic transition and microstructural properties in asputter deposited FeRh thin film system”, J. Appl. Phys., Vol. 74, p.3328, September 1993; C. Paduani, “Magnetic properties of Fe—Rh alloys”,J. Appl. Phys., Vol. 90, p. 6251, December 2001; and J. Thiele et al.,“Magnetic and Structural Properties of FePt—FeRh Exchange Spring filmsfor Thermally Assisted Magnetic Recording Media”, IEEE Trans. Magn.,Vol. 40, p. 2537 (2004).

In U.S. Patent Application Publication No. 2003/0108721 and in apublication by S. Koyama et al., “Reduction of coercivity in FePt—FeRhbilayer films by heating”, IEEE Trans. Magn., Vol. 41, p. 2854 (2005),the AFM-FM phase transition is shown to increase or decrease bycontrolling the seed layer and employing a FeRhX alloy where X can bePd, Pt, Ir, etc. Compositional control of the FeRhX material can alsoproduce as narrow as a 10° K to ˜20° K difference in AFM=>FM transitiontemperature during heating and FM=>AFM transition temperature duringcooling. In related U.S. Pat. No. 6,834,026, a TAMR disk is describedthat is comprised of a bilayer of an FM layer and a layer that switchesbetween FM and AFM states by a temperature change.

Referring to FIG. 1, an illustration of AFM=>FM transition curves takenfrom U.S. Patent Application Publication No. 2005/0281081 is shown fordifferent FeRh alloys with various compositions. This compositionmodifiable switching temperature and narrow transition windowtheoretically make the AFM/FM phase control of FeRh alloys easy torealize during actual write head operations.

The prior art references mentioned above that involve FeRh or FeRhXalloys are mainly focused on magnetic recording medium applicationswhere an FeRh alloy layer is part of the magnetic recording layer thatalso contains another hard magnetic material which has a very highanisotropy. A high anisotropy in the hard magnetic material is needed toenhance the recorded bit's thermal stability when the bit physical sizeis in the sub-micron range. However, the high anisotropy also makes themagnetization in the recording layer not easy to reverse during a writeprocess. Thermal heating of the FeRh induces an AFM to FM transition andthe resulting FM state of the FeRh is a soft material with very lowanisotropy. With the FM exchange between the hard magnetic layer and theFeRh layer, the FM phase of FeRh enables an easier reversal ofmagnetization in the recording layer during a write process. Heatassisted magnetic recording, also known as HAMR, has been a topic ofmajor interest in the prior art. A similar idea is utilized in a MRAMapplication in U.S. Patent Application Publication No. 2005/0281081where a data storage layer is also a hard material abutted with a FeRhlayer. The switching current field is easier to reverse by means of athermally induced FM phase in the FeRh layer.

Formation of a FeRh layer in the prior art usually involves relativelyhigh temperature (>400° C.) during deposition as described in theaforementioned Thiele reference, and typically includes anafter-deposition thermal treatment. This process which generally resultsin a bcc CsCl type FeRh crystalline structure is considered too harshfor commercial recording head fabrication. More recent methods are shownto form a bcc FeRh structure with lower substrate temperature andshorter annealing time and involve proper selection of seed layer andsubstrate as described by S. Maat et al. in “Temperature and fieldhysteresis of the antiferromagnetic-to-ferromagnetic phase transition inepitaxial FeRh films”, Phys. Rev. B, Vol. 72, p. 214432-1 (2005), oremploy an equi-atomic composition of Fe and Rh as described by S. Hashiet al., “A large thermal elasticity of the ordered FeRh alloy film withsharp magnetic transition”, IEEE Trans. Magn., Vol. 40, p. 2784 (2004).

Replacing a small percentage of the Rh atoms in the FeRh lattice with anequal amount of Pd, Pt, or Ir atoms could help to reduce the annealingtemperature and annealing time during a FeRhX alloy deposition without asignificant reduction in magnetic moment. With Pd, Pt, or Ir addition,the resulting FeRhPd, FeRhPt, or FeRhIr alloys can also reduce theFM=>AFM transition temperature down to about 100° C., making it morepractical for device applications. Besides conventional deposition andafter-deposition annealing, a multi-layer FeRh structure with mono-layerlevel Fe/Rh thickness and a bcc-like structure has been formed as shownby M. Tomaz et al., “Fe/Rh (100) multilayer magnetism probed by x-raymagnetic circular dichroism”, Phys. Rev. B, Vol. 57, p. 5474, September1997. A FeRh structure with an intrinsic AFM state is described by D.Spisak and J. Hafner in “Structural, magnetic, and chemical propertiesof thin Fe films grown on Rh (100) surfaces investigated with densityfunctional theory”, Phys. Rev. B, Vol. 73, p. 155428 (2006). Theseresults may provide an alternative way to synthesize a bcc FeRh thinfilm layer for AFM/FM transition.

In U.S. Pat. No. 6,410,170, a FeRh layer is used in a pole or shieldstructure of a write head.

A conventional PMR write head as depicted in FIG. 2 typically has a mainpole layer 10 with a pole tip 10 t at an air bearing surface (ABS) 5 anda flux return pole (opposing pole) 8 which is magnetically coupled tothe write pole through a trailing shield 7. Magnetic flux in the mainpole layer 10 is generated by coils 6 and passes through the pole tipinto a magnetic recording media 4 and then back to the write head byentering the flux return pole 8. The write pole concentrates magneticflux so that the magnetic field at the write pole tip 10 t at the ABS ishigh enough to switch magnetizations in the recording media 4. Atrailing shield 7 is added to improve the field gradient in thedown-track direction.

Referring to FIG. 3, a top view is shown of a typical main pole layer 10that has a large, wide portion called a yoke 10 y, a narrow rectangularportion 10 p called a write pole that extends a neck height (NH)distance y from the ABS plane 5-5 to a plane 3-3 parallel to the ABSwhere the pole intersects a flare portion 10 f at the neck 12. The flareportion 10 f adjoins the yoke along a plane 4-4 and flares outward fromthe plane 3-3 at an angle θ from a dashed line 11 that is an extensionof one of the long rectangular sides of the write pole 10 p. PMRtechnologies require the pole 10 p at the ABS to have a beveled shape(as viewed from the ABS) so that the skew related writing errors can besuppressed. A write head may also have a stitched pole configuration asdescribed in U.S. Pat. No. 6,826,015.

One disadvantage of prior art AFC lamination schemes is that thecoupling strength of a FeCo/Ru/FeCo configuration or the like istypically large and this type of AFC lamination will inevitably cause alarge anisotropy field and low magnetic moment under a low field.Although the coupling strength can be lowered by using a thickernon-magnetic layer (increasing Ru thickness from 7.5 to about 18Angstroms, for example), the magnetic moment will be diluted as thenon-magnetic content in the FeCo/Ru/FeCo stack is increased. Therefore,an improved lamination scheme for a write pole is needed that enables ahigh magnetic moment while simultaneously providing a mechanism toreduce remanence.

SUMMARY OF THE INVENTION

One objective of the present invention is to provide a laminated mainpole layer that reduces remanence during non-write operations tominimize pole erasure, and has a strong write field comparable to singlepole writers to achieve high writability.

Another objective of the present invention is to provide a flux gate inthe main pole layer to reduce remanent flux leaking from the yoke intothe write pole tip and thereby minimizing pole erasure caused by yokeremanence.

These objectives are realized in the present invention by providing alaminated main pole layer comprised of an AFM-FM phase change materialas a spacer layer in the lamination scheme. During non-write operations,the phase change material is in an AFM state that results inmagneto-static coupling to minimize remanence. The phase change materialmay be switched by heating to a FM state to promote a strong write fieldduring write operations. Localized heating may be provided by a smallheating coil in the write gap region near the write pole tip. The phasechange material may be FeRh or a FeRhX alloy where X is an elementincluding but not limited to Pd, Pt, and Ir.

In one embodiment, the entire main pole layer including yoke, flareportion, and write pole is laminated with a plurality of “n”ferromagnetic layers and “n−1” AFM-FM phase change material layersformed in an alternating fashion. There is a ferromagnetic layer formedat the top and bottom of the laminated stack and neighboringferromagnetic layers are separated by an AFM-FM phase change materiallayer that serves as a spacer. The planes of the layers areperpendicular to the ABS. Control of the AFM-FM transition occurs byheating and cooling from the writer coils and/or a local heater near thewrite pole at writing and non-writing conditions, respectively.Optionally, heating/cooling can be realized by a separate heating coilin the write gap region near the write pole tip.

A second embodiment is similar to the first embodiment except that aferromagnetic layer is added for additional flux on one or both sides ofthe laminated stack when viewed from a cross-track direction of thewrite head. From a perspective at the ABS plane, the ferromagnetic layeris added at the top and/or the bottom of the laminated stack. The one ortwo ferromagnetic layers are formed in the yoke portion and extend overa section of the flare portion but not over the write pole.

In a third embodiment, the PMR head is partially laminated. The yoke andall or a section of the flare portion are made of a single ferromagneticlayer while the write pole is comprised of a laminated stack having aplurality of “n” ferromagnetic layers and “n−1” AFM-FM phase changematerial layers arranged in an alternating fashion such that neighboringferromagnetic layers are separated by an AFM-FM phase change materialspacer. From a cross-track view where the ABS is at the bottom, thewrite head has a top ferromagnetic yoke portion directly above a bottomlaminated portion that includes at least the write pole tip portion.

A fourth embodiment is similar to the third embodiment except theferromagnetic yoke is not directly above the laminated portion but ispositioned on one side of the laminated stack from a cross track view toform a stitched pole structure. The flare portion of the main pole layerhas a first section made of a single ferromagnetic layer that iscoplanar with the yoke, and a second laminated section that adjoins thefirst section along one side. The second laminated section has the samewidth and thickness as the laminated write pole portion and connectswith the first section through a ferromagnetic layer. The laminatedstructure has a plurality of “n” ferromagnetic layers and “n−1” AFM-FMphase change material layers formed in alternating fashion.

In a fifth embodiment, the PMR head from a cross-track view has at leasta portion of the yoke and the entire write pole made of a singleferromagnetic layer. Between the write pole and the yoke is an AFM-FMphase change material layer that serves as a flux gate to preventremanence flux leaking from the yoke into the write pole. In one aspect,only the flare portion of the main pole layer is made of the AFM-FMphase change material. However, the present invention also encompassesan embodiment in which the flare portion and a section of the yoke thatadjoins the flare portion are made of an AFM-FM phase change material.As mentioned previously, AFM-FM transition is achieved byheating/cooling from the write coils at writing/non-writing conditionsor by thermal heating/cooling realized with a separate electrical paththat heats locally on the laminated portion of the write head withelectrical current.

In a sixth embodiment, the main pole layer has a stitched structure inwhich the yoke portion and a first section of the flare portion form asingle ferromagnetic layer. A second section of the flare portion andthe write pole have the same thickness and width and are comprised of anAFM-FM phase change material layer and a ferromagnetic layer. One sideof the AFM-FM phase change material layer in the second section adjoinsa side of the first section of the flare portion, and a side of theAFM-FM phase change material layer opposite the first section adjoinsthe single ferromagnetic layer in the write pole and second section ofthe flare portion. The AFM-FM phase change material layer may serve as aflux gate to prevent remanent flux from the yoke and first section ofthe flare portion from reaching the write pole tip.

There is a seventh embodiment similar to the sixth embodiment except thesingle ferromagnetic layer in the write pole and second section of theflare portion is replaced by a laminated structure comprised of “n”ferromagnetic layers and “n−1” AFM-FM phase change material layers thatare formed in an alternating fashion. The AFM-FM phase change materiallayer that contacts the first section of the flare portion may bethicker than the other AFM-FM phase change material layers in thelaminated stack.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plot from a prior art reference that shows magnetization ofFeRhX alloys vs. temperature in the form of AFM-FM transition curves.

FIG. 2 is a cross-sectional view of a conventional PMR writer showingthe main write pole, flux return pole, magnetic recording media, andcoils that generate magnetic flux.

FIG. 3 is a down track view of a main pole layer of a conventional PMRwrite head that shows the yoke, flare portion, and write pole portion,and a flare angle.

FIG. 4 a is a FEM simulation of a write field vertical component vs.down-track position for a laminated stack having a non-magnetic spacerand a magnetic spacer.

FIG. 4 b is a FEM simulation of a trailing edge vertical field vs. writecurrent for a laminated stack having a non-magnetic spacer and amagnetic spacer.

FIG. 4 c is a FEM simulation of maximum corresponding field (effectivefield) vs. write current for a laminated stack having a non-magneticspacer or a magnetic spacer.

FIG. 5 shows a cross-sectional view from the ABS plane of a write poleformed within an insulation layer on a substrate according to thepresent invention.

FIG. 6 a shows a down-track view (left) and cross-track view (right) ofa laminated PMR write head according to a first embodiment of thepresent invention, and FIG. 6 b is a cross-sectional view of a PMRwriter according to an embodiment of the present invention including awrite pole, flux return pole, heater element that can provide heating tothe write pole, and coils that generate magnetic flux.

FIGS. 7 a, 7 b show down-track views (left) and cross-track views(right) of a laminated PMR write head according to a second embodimentof the present invention.

FIG. 8 shows a down-track view (left) and cross-track view (right) of alaminated PMR write head according to a third embodiment of the presentinvention.

FIGS. 9 a, 9 b show simulated thermal profiles in a PMR write head whereheating is provided by a local heater coil and a Dynamic Fly Heater(DFH), respectively.

FIG. 10 is a down-track view (left) and cross-track view (right) of aPMR write head having a laminated stitched pole structure according to afourth embodiment of the present invention.

FIG. 11 shows a down-track view (left) and cross-track view (right) of amain pole layer in a PMR writer having an AFM-FM phase change materiallayer to minimize remanent flux from the yoke from reaching the writepole tip according to a fifth embodiment of the present invention.

FIG. 12 is a down-track view (left) and a cross-track view (right) of amain pole layer in a PMR writer in which an AFM-FM phase change materiallayer (flux gate) is formed between first and second sections of a flareportion of the yoke according to a sixth embodiment of the presentinvention.

FIG. 13 is a down track view (left) and a cross-track view (right) ofthe PMR write head in FIG. 11 where a single ferromagnetic layer in thewrite pole is replaced by a laminated structure having “n” ferromagneticlayers and “n−1” AFM-FM phase change material layers formed in analternating fashion according to a seventh embodiment.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is a PMR write head comprised of an AFM-FM phasechange material and a method of making the same. A design is describedwherein at least a section of the main pole layer comprised of yoke,flare portion, and write pole is made of an AFM-FM phase change materialto enable switching back and forth from a non-writing state that hasmagneto-static coupling between adjacent magnetic layers, and a writingstate having ferromagnetic coupling between adjacent magnetic layers. Asa result, magneto-static coupling between adjacent magnetic layers thatreduces magnetic remanence to minimize pole erasure can be switched byheating, mechanical, or electrical controlled changes to FM couplingwhich provides a strong write field to enhance writability. The presentinvention is not bound by any particular write pole shape as viewed fromthe ABS plane or a down-track view and thereby encompasses a variety ofshape designs as appreciated by those skilled in the art.

The inventors were motivated to improve the design of a PMR write headsince prior art laminated schemes that minimize remanent magnetizationin order to suppress pole erasure (PE) have a disadvantage in poorwritability. In particular, there is a trade-off between reducing PEfield and maintaining head field during writing mainly because thephysical mechanism (AFM or magneto-static coupling field) which isdesirable in a non-writing condition to help reduce PE field also existsin a writing operation where it is not desirable. The inventors haveovercome the intrinsic problem that exists in conventional laminatedwrite heads by employing an AFM-FM phase change material in the mainpole layer and in particular, as a spacer between adjacent ferromagneticlayers in a laminated scheme. However, the AFM-FM phase change materialmay also be formed between a FM layer in the yoke and a FM layer in thewrite pole to minimize flux leakage from the yoke to the write pole tipas described in various embodiments of the present invention.

It is known in the prior art that for a FeRh alloy at transitiontemperatures from 300° K to about 400° K, the AFM state magnetization isclose to zero and FM state magnetization can be more than 1000 emu/cc.According to the present invention, when an AFM-FM phase change materialsuch as FeRh or a FeRhX alloy is employed as a spacer layer in alaminated main pole layer, the low temperature AFM state is similar to aconventional non-magnetic material and the PE field is reduced byinter-layer magneto-static interaction. FeRh or a FeRhX alloy at a hightemperature FM state has a magnetization higher than Permalloy whichhelps increase the head field because of the FM state's large magneticmoment. Furthermore, the FM state promotes FM exchange coupling betweenadjacent magnetic layers and thereby increases the head field with theadditional contribution from the magnetic layers that results from abetter saturation of these magnetic layers.

Referring to FIG. 4 a, a finite-element (FEM) simulation demonstratesthe different effect of a non-magnetic spacer layer and a magneticspacer layer during a write operation. The results in curve 41 representa laminated PMR write head with a non-magnetic spacer similar to aconventional laminated main pole layer while curve 42 shows a laminatedPMR write head with a magnetic spacer that has a saturationmagnetization of 800 emu/cc and indicates the capability of a FeRh likeAFM-FM phase change material as a spacer that has a certainmagnetization during writing. The write pole has a 250 nm thickness anda 100 nm pole width. Eight equally separated pole spacer layers with athickness of 6 nm are used for the calculations. The write fieldvertical component amplitude is plotted as a function of the down-tracklocation. Although the highest field is the same for the non-magneticand magnetic spacer examples, the field level and field gradient at thetransition point (trailing edge) are obviously higher for the magneticspacer, indicating a better writability.

Referring to FIG. 4 b, the trailing edge vertical field is plotted as afunction of the write current amplitude for the non-magnetic spacer andmagnetic spacer examples. In FIG. 4 c, the maximum corresponding field(effective write field considering the field angle effect for aStoner-Wohlfarth type magnetic recording medium) is plotted as afunction of write current. In FIG. 4 b, the trailing edge vertical fieldfor the magnetic spacer example shows approximately a 1000 Oe writefield increase at 60 mA compared with the non-magnetic spacer. FIG. 4 cshows there is more than a 500 Oe higher effective write field for themagnetic spacer example at each current. Considering that the 800 emu/ccvalue is less than the maximum magnetization of FeRh reported in theprior art, the FeRh-like AFM-FM phase change spacer has the potential toenhance the write field even further. Additionally, if one takes intoaccount the FM exchange effect from the spacer in its FM state, which isnot included in the FEM simulation, the write field enhancement can bemore substantial.

According to the present invention, various embodiments of main polelayer having an AFM-FM phase change material in one or more sections ofa yoke, flare portion, or write pole are described. The AFM-FM phasechange material is used to minimize magnetic remanence and also enhancethe write field, particularly near the trailing edge.

Referring to FIG. 5, a view of the write pole 21 of a main pole layerformed within an insulation layer 50 according to the present inventionis depicted from an ABS plane. A substrate 18 is provided that may becomprised of AlTiC, for example. The substrate 18 may also be aninsulation layer formed on a top shield (not shown) in a mergedread/write head. In one embodiment, a RIE resistant layer 19 may beformed on the substrate 18 by a sputter deposition or physical vapordeposition (PVD) process, for example, and preferably is made of amaterial such as Ru or NiCr that has a high selectivity relative to aninsulating material such as alumina during a subsequent RIE etch thatuses BCl₃, chlorine, and fluorocarbon gases. Alternatively, the writepole 21 and main pole layer may be formed directly on the substrate 18or on a seed layer disposed on the substrate. Above the RIE resistantlayer 19 is an insulation layer 50 wherein a mold shape comprising anopening for the write pole (and main pole layer) is formed. Theinsulation layer 50 may be comprised of Al₂O₃ or silicon oxide that isdeposited by a PVD process, a sputtering technique, or the like in thesame deposition tool as the RIE resistant layer. The insulation layer 50may also be made of other dielectric materials known in the art. In anembodiment where the write pole 21 and main pole layer are sputterdeposited to fill the mold opening, the insulation layer 50 has athickness equivalent to the desired thickness of the main pole layer anda chemical mechanical polish (CMP) technique may be employed toplanarize the main pole layer including write pole 21. Optionally, themain pole layer and write pole 21 may be formed by first depositing oneor more magnetic layers on the substrate 18 with or without an etch stoplayer 19 by a sputter deposition process, for example. Then aphotoresist layer (not shown) is patterned on the main pole layermaterial followed by one or more etch steps that define the shape of thewrite pole 21 and main pole layer. Thereafter, the photoresist isstripped and the insulation layer 50 is deposited. A CMP process may beused to make the insulation layer 50 coplanar with the write pole 21 andmain pole layer.

In one embodiment of the present invention, the write pole 21 has atrapezoidal shape with sloped sidewalls 21 s wherein the top surface 21t of the write pole has a larger width along the ABS plane than thebottom surface 21 b. The width w may be referred to as the track width.Moreover, the sidewalls 21 s are sloped at an angle θ of about 5 to 20degrees with respect to the plane of the RIE resistant layer 19 (andsubstrate 18). The pole has a beveled shape with an angle θ so that theskew related writing errors can be suppressed. Note that during a writeoperation, the write pole 21 moves in a negative “z” direction such thatthe top surface 21 t is the trailing edge. The present invention alsoanticipates other write pole structures such as one where the topsurface 21 t has a concave shape that can be formed by performing anetching process on a trapezoidal shape.

Referring to FIG. 6 a, a first embodiment of the present invention isillustrated with a down-track view of a PMR write head 20 on the leftand a cross-track view on the right. The cross-track view is obtained byrotating the down-track view 90 degrees into the plane of the paperalong the axis 26-26. The PMR writer is comprised of a write pole 21having a write pole tip 21 t formed along the ABS (not shown), a flareportion 22 of a main pole layer that adjoins a side of the write poleopposite the ABS, and a yoke 23 that adjoins the flare portion along aside (not shown) opposite the write pole. In other words, the flareportion approximates a triangular shape, and the yoke may have arectangular or square shape as viewed from a down-track position. Theyoke 23 concentrates the magnetic flux and serves as a conduction pathof the magnetic field generated by the writer coils (not shown) on oneor both sides of the yoke. The flare portion 22 usually serves tofurther concentrate the flux from the yoke 23 into the write pole tip 21t. The back end of the yoke 23 is considered to be a side of the yokethat is farthest from the ABS.

An important feature is that the entire PMR head 20 is laminated with aplurality of “n” ferromagnetic layers 24 and “n−1” AFM-FM phase changematerial spacers 25. Preferably, there is a ferromagnetic layer 24 ateach side from a cross-track view and the ferromagnetic layers 24 andAFM-FM phase change material spacers 25 are arranged in alternatingfashion. The planes of the layers 24, 25 are oriented perpendicular tothe ABS 17-17. In the exemplary embodiment, the write pole 21, flareportion 22, and yoke 23 are coplanar and have the same thickness t ofabout 0.05 to 0.4 microns in a direction parallel to the ABS. In oneaspect, all of the ferromagnetic layers 24 have a same first thicknessin the “x” direction and all of the AFM-FM phase change material spacers25 have a same second thickness in the “x” direction of about 1 to 20nm. Preferably, the second thickness is less than the first thickness inorder to optimize the ferromagnetic content and the write field.Optionally, one or more of the ferromagnetic layers 24 may have athickness different than the other magnetic layers, and one or more ofthe AFM-FM phase change material spacers 25 may have a differentthickness than the other AFM-FM phase change material spacers.

The ferromagnetic layers 24 may be comprised of a material including butnot limited to CoFe, CoFeNi, CoFeN, and NiFe. The AFM-FM phase changematerial spacers 25 are preferably comprised of FeRh or a FeRhX alloywhere X is Pd, Pt, Ir, or the like and the Rh content is greater than 35atomic %. The AFM-FM phase change material spacers 25 are in an AFMstate when the PMR writer is not in a writing mode and are in a FM stateduring a writing operation. In one embodiment (FIG. 6 b), the transitionfrom an AFM to a FM state is accomplished by means of heating that isprovided by the writer coils 6. Alternatively, the AFM to FM transitionis realized by employing a separate resistive heater 42 or a separateheater coil 41 for heating the write pole tip portion of the main polelayer or the section of the main pole layer containing the AFM/FM phasechange material. In still another embodiment, the writing coils 6 and aseparate resistive heater or separate heater coil 41 are used to provideheating for the AFM-FM transitions. For example, a heater coil 41 may beformed within the write gap region 40 between the write pole 21 and theflux return pole 8. This type of local heating reduces thermalinterference between AFM-FM transitions in the PMR writer and control ofwriter/reader fly height. Typically, an AFM-FM phase change materialspacer 25 is in an AFM state when the temperature of the laminatedstructure is ≦370° K, or ≦70° C. above room temperature, and is in a FMstate when the temperature of the laminated structure is ≧400 K or about≧100° C. above room temperature. For example, the actual transitionpoint for a Fe₄₈Rh₅₂ alloy is between 70° C. and about 100° C. At anytemperature below the transition point, the AFM-FM phase change materialis in the AFM state. Transition from a FM state to an AFM state isaccomplishing by cooling in the writer coils and/or in the localizedheat source or resistive heater. Those skilled in the art willappreciate that a Dynamic Fly Heater (DFH) may be employed as aresistive heater 42 and may be located proximate to the back end 23 b ofthe yoke 23.

Referring to FIG. 7 a, a second embodiment is depicted that is similarto the first embodiment except a ferromagnetic layer 28 is added on oneside of the laminated main pole layer adjacent to a ferromagnetic layer24. The ferromagnetic layer 28 which is used to add magnetic flux to thewrite pole tip may be comprised of the same material as in ferromagneticlayers 24 and has a thickness s in the x-axis direction parallel to theABS 17-17 of 0.1 to 10 microns. The value of s may be greater than orless than that of thickness t depending upon the amount of added fluxdesired in the PMR writer 20. In FIG. 7 b, the second embodiment alsoencompasses a PMR writer configuration wherein a second ferromagneticlayer 28 having a thickness s₂ may be added to the side of the laminatedstructure (cross-track view) adjacent to a second ferromagnetic layer 24and opposite a first ferromagnetic layer 28 that has a thickness s₁ inan x-axis direction. From a cross-track view on the right side of thedrawing, the one or two ferromagnetic layers 28 in FIGS. 7 a, 7 b,respectively, should extend across the entire yoke 23 and over a sectionof the laminated structure in the flare portion 22, but not over thewrite pole 21. As illustrated in FIGS. 7 a, 7 b, the flare portion 22extends a distance a between the write pole 21 and the yoke 23 accordingto a down-track view on the left side of the drawings. However, aferromagnetic layer 28 does not cover the entire flare portion 22 butstops a certain distance b along the plane 27-27 which is at the end ofthe write pole 21 opposite the ABS 17-17. The s₁ thickness is notnecessarily the same as the s₂ thickness, and both s₁ and s₂ may begreater than or less than t depending upon the amount of additionalmagnetic flux desired. In the second embodiment, a ferromagnetic layer28 may be formed by an electroplating process while the laminatedstructure is formed by a sputter deposition process.

Referring to FIG. 8, a third embodiment is shown with a down-track view(left) and cross-track view (right) wherein the PMR writer 20 ispartially laminated. In particular, the yoke 23 is comprised entirely ofa single ferromagnetic layer 30 that may be made of the same magneticmaterial as in ferromagnetic layers 24. In addition, the ferromagneticlayer 30 extends into the flare portion and stops at a plane 29-29 thatis a distance c of about 0 to 10 microns from the end of the write pole21 that is opposite the ABS 17-17. When c>0, the write pole 21 and asection of the flare portion 22 adjacent to the write pole are made of alaminated structure comprised of alternating ferromagnetic layers 24 andAFM-FM phase change material layers 25 as described in the first twoembodiments. The ferromagnetic layer 30 has a thickness t in the x-axisdirection along a plane that is parallel to the ABS 17-17, and thelaminated structure in the write pole and adjacent section of the flareportion 22 has a thickness v along a plane parallel to the ABS that ispreferably less than t. In this embodiment, the yoke 23 is directlyabove the laminated structure, and one side of the ferromagnetic layer30 may be coplanar with a side of the laminated structure from across-track view. The laminated structure has a first end along the ABS17-17 and a second end opposite and parallel to the first end along theplane 29-29. Ferromagnetic layer 30 has an end that adjoins the secondend of the laminated structure, and a second end that corresponds to theback end 23 b of the yoke 23. Heating and cooling is achieved by writercoils and/or by a resistive heater or a localized heater source near thewrite pole tip.

Alternatively, when c=0, the laminated structure comprises only thewrite pole 21. The yoke 23 and flare portion 22 are made of a singleferromagnetic layer 30 formed above the laminated structure from across-track view. Note that the ferromagnetic layer 30 stops along theplane 29-29 which corresponds to the interface between the write pole 21and flare portion 22 at the front end of flare portion 22.

In the configuration shown in FIG. 8, a localized heating source ispreferred for several reasons. First, a small local heating coil in thewrite gap (not shown) near the write pole that is dedicated as a heatsource to drive the transitions between AFM and FM magnetic states inAFM-FM phase change material spacers 25 can provide a better and moreefficient temperature control than a conventional DFH resistive heaterthat is typically used to control both the reader actuation at read modeand writer actuation at write mode. The DFH is a resistor typicallylocated near the back end of the yoke in a conventional PMR writer andthe heating process causes the main pole layer to expand and push thewrite pole closer to the recording media. From FEM simulation results, asmall heating coil in the write gap region can deliver the thermalrequirement for an AFM=>FM transition with only 5.5 mW of power to givea 113.97° C. temperature at the write pole tip 21 t with a thermalgradient profile as depicted in FIG. 9 a. In contrast, a conventionalDFH uses 100 mW plus 40 mA write current to reach 80° C. at the writepole tip 21 t with a thermal gradient profile as shown in FIG. 9 b.Since the DFH is a greater distance from the write pole than the smallheating coil described herein, the DFH creates a lower temperature risein the write pole 21 where the main writing function occurs while ahigher temperature rise is produced in the yoke 23 where heating is lesseffective for driving AFM=>FM transitions.

A second advantage of a smaller localized heat source is that using alarger conventional DFH type heat source to heat the pole tip to anappropriate temperature for an AMF=>FM transition might result in anunacceptably large protrusion that could be greater than the flyingheight to cause touch-down to the recording medium. This issueessentially negates the feasibility of utilizing a conventional DFH nearthe write pole 21 for controlling an AFM=>FM phase change.

A third advantage of a localized heat source is lower power consumptionthan required for a DFH type heat source to produce the temperatureincrease necessary for an AFM=>FM transition.

Finally, a small heater design intrinsically has a shorter thermal risetime and shorter settling (cooling) time which has been measured atabout 250 μ-sec. This fast response is due to the proximity of the heatsource to the write pole tip and a lower volume of magnetic material tobe heated. Therefore, the small heater design should be especiallyadvantageous for a high data rate application with its fast responsetime.

Referring to FIG. 10, a fourth embodiment is depicted that is similar tothe third embodiment in that the PMR writer 20 has a partially laminatedconfiguration. However, in this case, the ferromagnetic layer 30 thatincludes the yoke 23 and a section of the flare portion 22 is notdirectly above the laminated structure comprised of alternatingferromagnetic layers 24 and AFM-FM phase change material spacers 25 butis offset to form a stitched pole configuration. The flare portion 22has a first section 22 a attached to an end of the yoke 23 and a secondsection 22 b attached to an end of the write pole 21 opposite the ABS.The first section 22 a preferably has the same thickness t as the yokeand extends a distance a from the yoke towards the write pole 21. Thesecond section 22 b overlaps the first section 22 a for a distance dalong a side that is perpendicular to the x-axis and ABS 17-17 and isparallel to the planes of the layers 24, 25 in the laminated structure.The second section 22 b has the same thickness v as the write pole 21 inthe x-axis direction parallel to the ABS 17-17 from a cross-trackperspective. Although the exemplary embodiment shows a>d, the presentinvention also anticipates a laminated structure wherein d=a and thesecond section 22 b has the same length as first section 22 a in adirection perpendicular to the x-axis. Preferably, the second section 22b connects with the first section 22 a through a ferromagnetic layer 24.In other words, the laminated structure has a first end along the ABS17-17 and a second end along the plane 31-31 parallel to the ABS. Thesurface of ferromagnetic layer 24 adjacent to the first section 22 arepresents the top surface of the laminated structure and the surface offirst section 22 a in contact with ferromagnetic layer 24 is considereda first side of the ferromagnetic layer 30 which connects a front end 22f of the flare portion 22 with the back end 23 b of the yoke 23.

Referring to FIG. 11, the present invention also encompasses a fifthembodiment in which an AFM-FM phase change material layer 25 a isemployed as a flux gate to prevent flux leakage from the yoke 23 to thewrite pole 21. In an AFM phase during a non-writing condition, the fluxgate has close to air magnetic permeability such that the write pole 21and yoke 23 are essentially magnetically separated. Therefore, theremanent magnetic flux from the magnetic domains or grains in the yoke23 are prevented from influencing the write pole tip 21 t and the PEfield can be substantially reduced in a non-writing condition. Besidesreducing magnetic remanence from the yoke 23, the flux gate while in anAFM phase also decreases the external field being conducted by the yokeand concentrated by the write pole 21 to minimize unwanted erasure.During a write operation, the flux gate is switched to a FM state andacts like a magnetic material with high permeability.

In one aspect, the AFM-FM phase change material layer 25 a has a lengthk perpendicular to the ABS 17-17 where k>a and comprises a section ofthe yoke 23 and the flare portion 22 between a plane 33-33 and plane32-32 that are both parallel to the ABS. The remainder of the PMR writer20 including write pole 21, and a section of yoke 23 and flare portion22 is comprised of a single ferromagnetic layer 30. The AFM-FM phasechange material layer 25 a has the same thickness t as the ferromagneticlayer 30 in the x-axis direction. Note that a section of flare portion22 adjacent to the write pole 21 is the ferromagnetic layer 30. Controlof the AFM=>FM transition in AFM-FM phase change material layer 25 a isprovided by thermal heating and cooling from the writer coils at writingand non-writing conditions, respectively, or with a separate electricalpath such as a coil that generates joule heating locally near the AFM-FMphase change material layer. The ferromagnetic layer 30 is preferablyformed by an electroplating operation and the AFM-FM phase changematerial layer 25 a may be formed by a sputter deposition process. Thefabrication process may involve a first photoresist mask (not shown) toassist in formation of the ferromagnetic layer 30 and a secondphotoresist mask to enable deposition of the AFM-FM phase changematerial layer 25 a.

Alternatively, k may be equal to a, and the fifth embodiment encompassesa PMR writer configuration wherein the size of the AFM-FM phase changematerial layer 25 a is reduced compared to that when k>a. In this case,the yoke 23 and write pole 21 are entirely comprised of ferromagneticlayer 30 while a section of the flare portion between the plane 34-34and 32-32 is comprised of the AFM-FM phase change material layer 25 ahaving a thickness t in the x-axis direction. A section of the flareportion 22 adjacent to the write pole 21 is also comprised of theferromagnetic layer 30.

Referring to FIG. 12, a sixth embodiment is illustrated which is similarto the stitched pole configuration in the fourth embodiment except thelaminated structure of alternating ferromagnetic layers 24 and AFM-FMphase change material spacers 25 in the second section 22 b and writepole 21 is replaced by a composite structure comprised of a singleAFM-FM phase change material layer 25 a with thickness e in the x-axisdirection and a ferromagnetic layer 36 having thickness f wherein f ispreferably larger than e. Ferromagnetic layer 36 may be made of the samematerial as in ferromagnetic layer 30. The AFM-FM phase change materiallayer 25 a is formed in a portion of second section 22 b and write pole21 that faces the ferromagnetic layer 30 and acts as a flux gate toprevent flux from yoke 23 and the first section 22 b of the flareportion from reaching write pole 21 during a non-write operation. Thus,the AFM-FM phase change material layer 25 a is in an AFM state duringnon-writing conditions and is in a FM state during a write process.Control of the AFM-FM transitions is enabled by thermal heating/coolingfrom writer coils or from a localized heat source as describedpreviously.

Referring to FIG. 13, a seventh embodiment is depicted that is similarto the sixth embodiment except the ferromagnetic layer 36 in the secondsection 22 b and write pole 21 is replaced by a laminated structurecomprised of a plurality of “n” ferromagnetic layers 24 and “n−1” AFM-FMphase change material spacers 25 formed in an alternating fashion asdescribed in previous embodiments. Furthermore, the AFM-FM phase changematerial layer 25 a adjacent to the first section 22 a may be thickerthan the AFM-FM phase change material spacers 25 and serves as a fluxgate to prevent flux from the yoke 23 and first section 22 a of theflare portion 22 from reaching write pole 21 and thereby minimizes poleerasure during non-writing conditions. The top of the AFM-FM materialphase change layer 25 a and laminated structure is formed along a plane37-37 at a distance g from the ABS 17-17. Control of the AFM-FMtransitions in AFM-FM phase change material layer 25 a and in AFM-FMphase change material spacers 25 is enabled by thermal heating/coolingfrom writer coils and/or from a resistive heater or from a localizedheat source as described previously.

It should be understood that after the main pole layer is formed, one ormore annealing processes such as hard axis annealing, easy axisannealing, or combinations of both hard axis and easy axis annealing maybe employed. Moreover, a planarization process such as a chemicalmechanical polish (CMP) step may be performed to smooth one or moresurfaces of the main pole layer during the fabrication process.

We have disclosed several embodiments of a PMR writer that takeadvantage of an AFM-FM phase change material layer and/or spacer in alaminated scheme to control magnetic remanence through AFM couplingduring a non-writing condition, and which optimize the write fieldduring a write operation through a FM contribution to improvewritability compared with conventional laminated PMR write heads.Fabrication of the various embodiments is achieved by well knownphotolithography, etching, and sputter deposition techniques. Forexample, a stitched write head may be fabricated by first forming a yokeand a first section of the flare portion and then in a subsequentsequence of steps, a second section of the flare portion and write poleare formed such that the second section is adjacent to the firstsection. This unique combination of magnetic remanence suppressionduring non-writing and maximization of write field during writing hasnot been achieved in the prior art to our knowledge.

While this invention has been particularly shown and described withreference to, the preferred embodiment thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade without departing from the spirit and scope of this invention.

We claim:
 1. A perpendicular magnetic recording (PMR) head comprised ofa main pole layer that includes a yoke, flare portion, and write poleportion with a write pole tip at air bearing surface (ABS), said mainpole layer consists of a laminated structure having a plurality of “n”ferromagnetic layers and “n−1” AFM-FM phase change material spacersarranged in an alternating manner and with planes that are oriented in alengthwise direction perpendicular to the ABS, the laminated structurehas a top surface and bottom surface that are essentially parallel toeach other, and said AFM-FM phase change material spacers can beinterchanged between antiferromagnetic (AFM) and ferromagnetic (FM)phases by application of thermal heating and cooling, and are in an AFMphase when the PMR recording head is in a non-writing mode and are in aFM phase during a data writing operation.
 2. The PMR head of claim 1wherein the yoke, flare portion, and write pole portion all have athickness of about 0.05 to 0.4 microns.
 3. The PMR head of claim 1wherein the “n” ferromagnetic layers all have a first thickness, and the“n−1” AFM-FM phase change material spacers all have a second thicknessbetween about 1 and 20 nm.
 4. The PMR head of claim 3 wherein the firstthickness is greater than the second thickness.
 5. The PMR head of claim1 wherein the AFM-FM phase change material spacers are comprised of FeRhor a FeRhX alloy where X is Pd, Pt, or Ir and the Rh content is greaterthan 35 atomic %.
 6. The PMR head of claim 1 wherein the ferromagneticlayers are comprised of CoFe, CoFeNi, CoFeN, or NiFe.